Five senior investigators will study the genetic control and molecular mechanism of immunoglobulin production, the synthesis and structure of the major histocompatibility and Ia antigens of the mouse, the functions of T and B cells and macrophages, the interaction of viruses with lymphoid cells, and the cellular basis for the immunologic defects in a number of human diseases. Wherever possible, continuous cell lines and variants derived from them will be used in order to learn more about the biology of lymphoid cells.